There's only one place on the cap that you can reference if the rotor is out of phase and you ain't usin it.
Really weird ignition issue...
- Thread starter Kern Dog
- Start date
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Dave999
Well-Known Member
i think.....but am not sure that the phasing is set up so that everything comes into best alignment between mid advance and total advance
low rpm, long dwell, biggest spark energy, can jump a longer distance from rotor tip to cap contact with less impact at the plug. jumps to closest rather than close cap contact
at hi rpm under load, dwell is limited by rpm, has impact on spark energy, closer alignment needed between rotor and cap contact to avoid mis fire and maximise spark at plug without wasting too much jumping a slightly bigger distance.
and i say i think because it impacts which end of travel you adjust when recurving a dissy.
do you take advance away from the advance range, by advancing the return position to decrease total advance or do you limit it at the total advance end...can't remember, i knew this cos i did it, but if could remember id be more confident in what i say above
i do know doing it the wrong way can leave the long loop spring doing nothing...
so its probably the starting point that is altered rather then the end.
Based on my own limited distributor fiddling i don't think they are set up with the "best" positioning for reluctor and rotor at stationary or for low rpm.
or my distributor was a "wrongun"
turning the reluctor over does impact phasing. a reluctor peak to the right of the pin will be to the left of it with the reluctor tuned upside down from its current position. the tiny pin position on the shaft is hard coded to the rotor position on the shaft but the reluctor can go onto that pin either way....... or it can on mine.... i'll have to qualify it with that, cos mine is a bosch made chrysler style distributor. not a chrysler/mopar distributor, yours may differ.
Dave
low rpm, long dwell, biggest spark energy, can jump a longer distance from rotor tip to cap contact with less impact at the plug. jumps to closest rather than close cap contact
at hi rpm under load, dwell is limited by rpm, has impact on spark energy, closer alignment needed between rotor and cap contact to avoid mis fire and maximise spark at plug without wasting too much jumping a slightly bigger distance.
and i say i think because it impacts which end of travel you adjust when recurving a dissy.
do you take advance away from the advance range, by advancing the return position to decrease total advance or do you limit it at the total advance end...can't remember, i knew this cos i did it, but if could remember id be more confident in what i say above
i do know doing it the wrong way can leave the long loop spring doing nothing...
so its probably the starting point that is altered rather then the end.
Based on my own limited distributor fiddling i don't think they are set up with the "best" positioning for reluctor and rotor at stationary or for low rpm.
or my distributor was a "wrongun"
turning the reluctor over does impact phasing. a reluctor peak to the right of the pin will be to the left of it with the reluctor tuned upside down from its current position. the tiny pin position on the shaft is hard coded to the rotor position on the shaft but the reluctor can go onto that pin either way....... or it can on mine.... i'll have to qualify it with that, cos mine is a bosch made chrysler style distributor. not a chrysler/mopar distributor, yours may differ.
Dave
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There's only one thing that can control the rotor phasing on a standard style Mopar distributor and that's the length of the vacuum advance arm. The advance can is what changes the rotor phasing as it pulls the breaker plate. So if it's out of phase, you either lengthen or shorten the vacuum advance arm to line the rotor up at idle. But you cannot "just choose" an arbitrary spot on the distributor as a reference. You must use the distributor cap alignment tab in relation to #1 on the cap.
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Dave999
Well-Known Member
Ok, but i thought you could get reluctors with 3 pin positions? lets you adjust the angle between a peak at the centre of the pickup and where the rotor arm points, that must come into play even If just a small amount. maybe enough to put anything added by the vacuum into the realm of too much....
granted i'd need one in the vice in front of me with a degree wheel to get my head straight on this again
messed with mine years ago. once it works you don't go back
Dave
granted i'd need one in the vice in front of me with a degree wheel to get my head straight on this again
messed with mine years ago. once it works you don't go back
Dave
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Who on EARTH would wanna go to that trouble when you can change the length of the advance can arm? Just SO much easier.Ok, but i thought you could get reluctors with 3 pin positions? that must come into play even If just a small amount. maybe enough to put anything added by the vacuum into the realm of too much....
granted i'd need one in the vice in front of me with a degree wheel to get my head straight on this again
messed with mine years ago. once it works you don't go back
Dave
Dave999
Well-Known Member
dunno but you can as far as i know...
the relationship between a reluctor peak aligned at the pickup and the direction of the rotor tip can be altered by a few degrees this way or that....
if the pin in the reluctor aligns with a peak right way up or upside down makes no difference but if doesn't it will.... and upside down reluctor would alter at least one characteristic
presume the 3 hole ones are designed as multifit covering 73 onwards distributors for all applications, one of 3 or 6 compromises will be the best
gotta chop 360* by I4 I/6 or V8 to cover all of the engines think you can get 3 position ones only for v8 applications
dave
the relationship between a reluctor peak aligned at the pickup and the direction of the rotor tip can be altered by a few degrees this way or that....
if the pin in the reluctor aligns with a peak right way up or upside down makes no difference but if doesn't it will.... and upside down reluctor would alter at least one characteristic
presume the 3 hole ones are designed as multifit covering 73 onwards distributors for all applications, one of 3 or 6 compromises will be the best
gotta chop 360* by I4 I/6 or V8 to cover all of the engines think you can get 3 position ones only for v8 applications
dave
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I believe the reluctor is offset and you cannot install it upside down.
Dave999
Well-Known Member
not an issue then.....
as i say so long ago
as i say so long ago
Dave999
Well-Known Member
here is one with 2 pin holes that are not 180 apart....
one position aligned with a peak and one slightly advanced or retarded,
could potentially cause a problem one way and not the other.
one position aligned with a peak and one slightly advanced or retarded,
could potentially cause a problem one way and not the other.
The phasing is close enough to work until the vac advance is applied causing a misfire. In a correctly phased distributor the rotor tip is slightly away from the distributor terminal and as vacuum is applied it is pulled towards the terminal and at full advance can land slightly past the terminal. If the distributor is incorrectly phased at the past the correct terminal position to start with and vac advance is applied it will pull the rotor away from the correct terminal and toward the terminal next to it. I suspect this is what is happening in his case. Incorrect phasing can be caused by several problems. Incorrect reluctor placement, Incorrect pick up coil placement, Incorrect rotor placement, Incorrect cap placement, reversed polarity on the pick up coil, and etc.
I suppose in hind site you could have just unpluged the vac advance hose allowing it to leak freely. This would simulate worst case scenario vacuum leak at the diaphragm. Usually on an otherwise smoothly idling engine with the line plugged, it will cause the motor to raise in idle speed slightly and maybe run a little rougher. Not run in the way you described with it plugged in. No way to know for sure at this point.
Not sure what you did there. There is only one way I know of to determine phasing. That is to use a timing light and preferably a simple one with no "dial up" feature, and determine when the spark actually happens in relation to the rotor. You need to cut/ drill an old cap so you can see the rotor and mark the position of the no1 tower, then spin it either in engine or with a drill, firing an ignition system. The timing light will flash at the point the spark fires, and the light will "stop" the photo in your brain of the rotor passing the cap tower
It's pretty simple, there are 2 slots on the reluctor wheel, 1 for small block and 1 for big block phasing.
Some wheels have rotation direction arrows.
Some wheels have rotation direction arrows.
Notice how one slot is 100% aligned with the center of a reluctor point and the other is not. Wrong slot could certainly cause the issue.
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AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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64 posts.
do it this way. no do it that way. no, that's not the way, here, do it my way.
I can't believe something so simple got to be so complicated.
With the distributor out, this should have been a two minutes or less diagnoses.
With the distributor still installed, it takes a bit longer simply because it's harder to get up in there to see.
Do you want me to write another novel to explain it?
Wait, I'm asking the OP!
do it this way. no do it that way. no, that's not the way, here, do it my way.
I can't believe something so simple got to be so complicated.
With the distributor out, this should have been a two minutes or less diagnoses.
With the distributor still installed, it takes a bit longer simply because it's harder to get up in there to see.
Do you want me to write another novel to explain it?
Wait, I'm asking the OP!
Yeah we all need you to swoop in and save the day. We're all too stupid, evidently.
oh how magnanimous of you!
please all knowing and great king of the far north, bestow your wonderous knowledge and savvy upon us, the great unwashed masses, for we live only to read your magnificent prose!
<snort>
one slot is aligned for the big block.
So they say. Still possible to get one installed in the wrong slot.
Yea it's 50/50.
mopowers
Well-Known Member
The 340 in my '68 Dart was acting similar to Kern's suddenly a few years ago. Turned out the roll pin locating the reluctor in the in the MP distributor had somehow worked it's way down allowing the reloctor to turn slightly. It was popping and coughing all the way home. Luckily I was only a mile or so from home and I was able to limp it home. It was a good lesson in how important the position of the reluctor is.
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mopar head
DoD nuisance Alien/Squatch extermination team
Kern, if you put your finger over the port on the mighty vac, squeeze the handle once it should hold vacuum. If not, it`s leaking elsewhere, they are a handy tool.
For all the years that I've been tinkering, I don't recall having many issues with the distributor, at least in LA engines.
If I had this happen several times before, I would have had no reason to post a thread asking about it. I'm happy to see input from others that have dealt with it too.
Thanks, I did do that and it does hold, though the method to get it to hold seems strange. I read the booklet but didn't see it clearly explained. Intuitively, I would expect it to work like a fuel pump or vacuum pump, being a one way valve only with a check valve so as it sucks in vacuum, you could release the handle/trigger and it would hold. This one does not do that. I had to squeeze the handle fully, then release it part way to find the spot where it would hold in the vacuum. Even then, it didn't peg the gauge.
I tried it with the included hose attached and without. Maybe this one works as designed but again, it was bought in 1998 which is 27 years ago. 27 years of sitting in a box, barely being used.
Both vacuum cans that I tested did hold but it gets weirder...
The distributor that was acting up would only get to 5-6 and then drop as I released the handle. The one I swapped in went to 10. I tested them before finding that the Mityvac only held vacuum with the handle in a specific position. I have not gone out to retest either distributor now that I know the quirky function of this pump.
I do have a curious mind but in this case, I'm not that interested in looking for a problem that seems to be solved.
The car ran fine with no vacuum advance but I wanted to attach it for the sake of efficiency. Doing so revealed a problem that realistically could have been related to the vacuum advance unit. It sure seems like connecting the vacuum line revealed a weakness elsewhere. To blame this issue on the vacuum advance would be like blowing up a 400,000 mile engine after running a 300 HP shot of nitrous, then blaming the failure on the nitrous rather than the fact that the engine was barely holding it together beforehand.
Thank you for those that cared to respond. I appreciate those that took time to help since I too like to step in and give advice where I can...but it will help us all if you understand that you can't expect others to do exactly what you suggest. Sometimes those that are receiving the advice may somehow miss a comment or forget...then they get blasted for not doing it exactly the way that was suggested.
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